1. Field of the Invention
The present invention relates to a display device, and more particularly to a self-light-emitting display device having the improved viewing angle characteristics.
2. Description of the Related Art
A light-emitting device which uses light emission from electroluminescence elements (light-emitting elements) has been attracting attention as a display device with a wide viewing angle and low power consumption.
As a driving method of the light-emitting device which is mainly used for image display, there are an active matrix driving method and a passive matrix driving method. As for the light-emitting device using the active matrix driving method, emission/non-emission or the like of a light-emitting element can be controlled in each pixel. Therefore; it can be driven with lower power consumption than the passive matrix light-emitting device. Thus, the light-emitting device can be suitably mounted as a display portion of a compact electronic appliance such as a portable phone as well as a display portion of a large-screen television receiver set and the like.
In the active matrix light-emitting device, a circuit for controlling the drive of each light-emitting element is provided for each light-emitting element. The circuit and the light-emitting element are provided over a substrate so that the light emitted outside is not blocked by the circuit. In addition, in the portion overlapping the light-emitting element, light-transmissive insulating films are provided in stacked layers, through which light travels to be emitted outside. Such insulating films are provided for forming a circuit element such as a transistor and a capacitor as a main circuit component, or a wiring.
When light travels through the stacked insulating films, there might be a case where light reflected on the interface between each layer interferes with each other (called multiple interference) due to the difference in refraction factor of each insulating film. As a result, emission spectrum changes dependently on the angle seen from the emission side, leading to the inferior viewing angle characteristics.
For example, Patent Document 1 discloses a light-emitting device which is proposed in response to a problem that the visibility and the viewing angle characteristics degrade due to the difference in refraction factor of each layer, through which light emitted from a light-emitting element travels. The light-emitting device can avoid such a problem by defining the relationship of refraction factors between each layer.
[Patent Document 1]
Japanese Patent Laid-Open No. 2003-133062
Patent Document 2 discloses a light-emitting element as a display element, which is proposed in response to a problem that the viewing angle characteristics degrade in a light-emitting element having a resonance structure which is constituted by electrodes and a light-emitting layer. The light-emitting element can solve such a problem by improving the resonance structure.
[Patent Document 2]
Japanese Patent Laid-Open No. 2002-367770
However, in the structure of Patent Document 1, it is quite difficult to select materials which can satisfy both the desired refraction factor and the function of each layer such as an insulating property and a passivation property since the refraction factor is an intrinsic value to each material.
In addition, in the structure of Patent Document 2, only a light-emitting element is focused on, which is constituted by opposed electrodes and an organic layer interposed between them. Therefore, there is a possibility that the degradation of the viewing angle characteristics cannot be sufficiently suppressed in a light-emitting device such as an active matrix light-emitting device where light is emitted outside through a plurality of layers in addition to the light-emitting element.